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The Code Project Cofounder
Microsoft C++ MVP





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cheers,
Chris Maunder
The Code Project Cofounder
Microsoft C++ MVP






Hi everybody, i'm developing a Modified Compress Sparse Row Matrix Class (in C++, but i think this is not important for the algorithm) you can read a short explanation of the method here I wrote the constructor as follow :
template <typename T>
constexpr MCSRmatrix<T>::MCSRmatrix( std::initializer_list<std::initializer_list<T>> rows)
{
this>dim = rows.size();
auto _rows = *(rows.begin());
aa_.resize(dim+1);
ja_.resize(dim+1);
if(dim != _rows.size())
{
throw InvalidSizeException("Error in costructor! MCSR format require square matrix!");
}
itype w = 0 ;
ja_.at(w) = dim+2 ;
for(auto ii = rows.begin(), i=1; ii != rows.end() ; ++ii, i++)
{
for(auto ij = ii>begin(), j=1, elemCount = 0 ; ij != ii>end() ; ++ij, j++ )
{
if(i==j)
aa_[i1] = *ij ;
else if( i != j && *ij != 0 )
{
ja_.push_back(j);
aa_.push_back(*ij);
elemCount++ ;
}
ja_[i] = ja_[i1] + elemCount;
}
}
}
and it works well ! I also wrote a findIndex(i,j) method that return the value at i,j of the whole matrix and it works fine, so i'm able to print out the whole matrix using the operator overloading () who return 0 if in this position the element is zero otherwise the right value
template <typename T>
std::size_t constexpr MCSRmatrix<T>::findIndex(const itype row , const itype col) const noexcept
{
assert( row > 0 && row <= dim && col > 0 && col <= dim );
if(row == col)
{
return row1;
}
int i = 1;
for(int i = ja_.at(row1)1 ; i < ja_.at(row)1 ; i++ )
{
if( ja_.at(i) == col )
{
return i ;
}
}
return 1;
}
the operator is defined as :
template <typename T>
const T MCSRmatrix<T>::operator()(const itype r , const itype c) const noexcept
{
auto i = findIndex(r,c);
if( i != 1 && i < aa_.size() )
{
return aa_.at(i) ;
}
else
{
return 0.0 ;
}
}
Now I need to write an alghoritm that give 2 index of position is able to insert in the 2 vector the element in the right position could you help me about ?
I wrote this one but dosn't works fine !
template<typename T>
auto constexpr MCSRmatrix<T>::insertAt(itype row ,itype col , T elem) noexcept
{
if(elem == 0)
{
std::cerr << "zero element to insert ! Exit 1" << std::endl;
}
int index = findIndex(row,col);
if( index >= dim+1  row == col)
{
aa_.at(index) = elem ;
}
else if(index == 1)
{
for(auto i=row; i< dim+1 ; i++)
{
ja_.at(i) += 1 ;
}
if(ja_.at(row) >= aa_.size() )
{
aa_.push_back(elem);
ja_.push_back(col);
}
else if ( ja_.at(row) < aa_.size() )
{
ja_.insert(ja_.begin() + dim + row , col );
aa_.insert(aa_.begin() + dim + row , elem);
}
}
}
I hope you give me a way to write down the correct way to inert element ! thanks in advance
P.S. itype is a typedef of std::size_t !





I am developing a project that is meant to improve feature smoothness in heightmaps that represent terrain from multiple maps at different resolutions from satellite imagery.
I know how to use the data in the maps to detect the shorelines. What I want to do however is turn shorelines into edges (lines) that do not intersect at all so that I can smooth them from the blocky look they have outside the USA where satellite resolution is not as good. Most of the time this is fairly straightforward but the lack of good resolution on some of the height maps may result in islands touching the coastline. I want to make sure that the coast on the island follows the outline of the island while the main coastline stays the main coastline. Basically I believe this would boil down to making sure they don't intersect. This area of programming is completely new to me. I want to understand the best algorithm for 'untangling' intersections when more than one coast line happens to touch.





A question arose here at work where they would like to find datagaps in timeline datasets. This can be from database or from images. (eg each 6 hours there's an image).
Basically they want a "pseudocode" function that would work across technologies.
in: at least an array of datetime stamps
out: a list of gaps in the list.
This is what I have so far (it's C type language, but no language in particular):
function FindGaps(DateTime dts_start, DateTime dts_end, int amount, string interval, Array list2check){
Array listreference<DateTime, boolean>;
for(DateTime dts = dts_start; dts < dts_end; dts += amount (interval)){
listreference.Add(dts, false);
}
for(int i = 0; i < list2check.length; i++){
if(KeyExists(listrefence, list2check[i])){
listrefence[list2check[i]]) = true;
}
}
return listrefence;
}
and some of my own thoughts:
problems/remarks:
* You cannot uniformally convert months, years, ... eg to milliseconds (january has different amount of milliseconds than february, ...)
* not all datasets have uniform progression (timegap difference between points)
* datasets passed should not be too large
* the key check should be on similar interval (minutes = minutes eg. 00:00 = 00:00, but 00:00 != 00:00:01)
* adding the fill value can also mark the gap as true / false / invalid eg.
* should you "remove" values that are in between gaps? eg. there are 100 values in a row = false. Should we only keep first and last value?
* This will not be very fast: can we loop from start > end with amount (interval) and check if DateTime is in list2check? (how will we return?)
* better would be if there are points in between 2 points of the reference list, but how to do that practically? (could potentially fix point 2 to some extent)
Does anyone have experience in this? any tips or pointers?
(PS: I have a nice query that can do this in a (postgresql) database, but this does not fit file based datasets)
thanks!





I'm not sure I completely grok what you're trying to do, but what's wrong with comparing the difference between consecutive timestamps with your "required" interval?
Software rusts. Simon Stephenson, ca 1994. So does this signature. me, 2012





Put all your "samples" in a queue.
Pop the first sample; that is your starting date/time.
"Predict" the next sample by adding the samplying rate.
"Peek" into the queue to see if your prediction was right: if not, add prediction to "missing", else pop the predicted value from the queue.
Repeat until queue exhausted.
(Memory streams can also be employed; keeping "positioning" in mind).
"(I) am amazed to see myself here rather than there ... now rather than then".
― Blaise Pascal





In its "Prefix sum" section, Codility proposes the following problem. I don't see how to solve it within the constraints, that are O(N+M), and O(N) for space complexity. I know I should use the prefix sum technique, but I would need more hints. I'd like to not be given the solutions, but hints that would help me guide my thought process.

A DNA sequence can be represented as a string consisting of the letters A, C, G and T, which correspond to the types of successive nucleotides in the sequence. Each nucleotide has an impact factor, which is an integer. Nucleotides of types A, C, G and T have impact factors of 1, 2, 3 and 4, respectively. You are going to answer several queries of the form: What is the minimal impact factor of nucleotides contained in a particular part of the given DNA sequence?
The DNA sequence is given as a nonempty string S = S[0]S[1]...S[N1] consisting of N characters. There are M queries, which are given in nonempty arrays P and Q, each consisting of M integers. The Kth query (0 ≤ K < M) requires you to find the minimal impact factor of nucleotides contained in the DNA sequence between positions P[K] and Q[K] (inclusive).
For example, consider string S = CAGCCTA and arrays P, Q such that:
P[0] = 2 Q[0] = 4
P[1] = 5 Q[1] = 5
P[2] = 0 Q[2] = 6
The answers to these M = 3 queries are as follows:
The part of the DNA between positions 2 and 4 contains nucleotides G and C (twice), whose impact factors are 3 and 2 respectively, so the answer is 2.
The part between positions 5 and 5 contains a single nucleotide T, whose impact factor is 4, so the answer is 4.
The part between positions 0 and 6 (the whole string) contains all nucleotides, in particular nucleotide A whose impact factor is 1, so the answer is 1.
Write a function:
def solution(S, P, Q)
that, given a nonempty zeroindexed string S consisting of N characters and two nonempty zeroindexed arrays P and Q consisting of M integers, returns an array consisting of M integers specifying the consecutive answers to all queries.
The sequence should be returned as:
a Results structure (in C), or
a vector of integers (in C++), or
a Results record (in Pascal), or
an array of integers (in any other programming language).
For example, given the string S = CAGCCTA and arrays P, Q such that:
P[0] = 2 Q[0] = 4
P[1] = 5 Q[1] = 5
P[2] = 0 Q[2] = 6
the function should return the values [2, 4, 1], as explained above.
Assume that:
N is an integer within the range [1..100,000];
M is an integer within the range [1..50,000];
each element of arrays P, Q is an integer within the range [0..N − 1];
P[K] ≤ Q[K], where 0 ≤ K < M;
string S consists only of uppercase English letters A, C, G, T.
Complexity:
expected worstcase time complexity is O(N+M);
expected worstcase space complexity is O(N), beyond input storage (not counting the storage required for input arguments).
Elements of input arrays can be modified.
modified 6Nov17 5:26am.





S is a string; or an array of characters; characters which "convert" to impact numbers.
P and Q are (3) "substring ranges" into S.
The subset / substring of S will contain one or more "MIN" impact numbers.
"(I) am amazed to see myself here rather than there ... now rather than then".
― Blaise Pascal





hi,
im pretty rusty with algorithms and i was posed this question. how do I find the most amount of pages i can buy from a list of books within a certain budget. I got as far as sorting the list based on cost, then by no. pages. then i was thinking of creating a map with the cost as key and a list of books at each price. then sorting each keys list based on no of pages. I think im headed in the right direction but iam not quite sure how to complete the exercise? can someone help me of point me in the direction of the correct algorithms i should be using? cheers!





This is homework, and we don't do that for you  it's an exercise to get you thinking about problems, and working out how to solve them. If we give you the "correct algorithm" then that defeats the point of giving you the homework!
So instead, sit down with a pencil and paper, and work out how you would do it for yourself manually.
Hint: would knowing the price per page help you come up with a solution?
Bad command or file name. Bad, bad command! Sit! Stay! Staaaay...
AntiTwitter: @DalekDave is now a follower!





its not homework. its something im trying to implement in an android app im building! its an algorithm for an in built calculator to check how many pages i can buy from a list of comics from the marvel api.





You at first have to think about what is important for you :
 a special order
 lowest rest money
 maximum count of books
Dependent on this selection you would build different List's.
To be able to decide which List could be the best you must build different SubLists  example :
 you have 100 € and you could buy Book 1 (40 €), Book 2 (35 €), Book 3 (45 €), Book 4 (20 €)
 now one List could be Book 1,2,4  another one could be Book 2,3,4  or Book 1,3 ...
Now ... which List contains the best results for you ?





its based on most pages in a book that i can buy for a certain budget. think its the 0/1 knapsack problem.





Hi, I have 4 arrays 1, 2, .. N_{i} (i=14). N_{i} are fixed and very big. Every time I need to sample without replacement from each of them. The sample sizes (say M) are same for the 4 samples and are fixed and big as well (so N_{i} is bigger than M). I then calculate a single number (say X) using these 4 samples, which takes long time (normally 58 hrs). I need to find a 4sample set which minimizes X. What is the best search strategy? Thanks in advance.
modified 5Nov17 6:01am.





Hi folks, I've tried Googling for an answer to this but keep getting directed down network load balancing which, although related, is not my scenario.
My scenario: I have 3 products (x,y and z) which take 2000, 4000 and 5000 labour hours to assemble respectively. If I want to produce say 50 of product x, 40 of product y and 60 of product z in a year is there an algorithm for distributing the production (the loading) so that the labour hours are spread as evenly as possible throughout the year? I'm quite happy to be offered some additional reading / guidance or a general solution (teach a man to fish etc.).
That's always assuming there is an answer of course .
Andy B
modified 1Nov17 11:21am.





I am not sure whether this is what you want, but I really think you need to learn some cost/lost functions to decide how to manage the resources to minimize the cost and maximize the outputs. If I had paid any more attention to the class, I would have learnt how the maximization or cost reduction algorithms work, but... Cost function  Wikipedia.
Following resources will help you in understanding the overall algorithm, then write your own,
Cost Function  Coursera.org
Mathematical optimization  Wikipedia
The sh*t I complain about
It's like there ain't a cloud in the sky and it's raining out  Eminem
~! Firewall !~





Thanks Afzaal, the cost function is certainly what I'd like to end up with but when I look into the articles it quickly gets to a level of mathematical notation that I'm not comfortable with, despite being an engineering graduate (long time ago though).
I think in this case I'm going to have to approximate something by working out each products weekly average, then phase shifting them by a number of days each and see if I can derive a function from this somehow. It won't be optimal but then realworld production usually isn't .
The links reference some fascinating material though, it's certainly an area I'd like to explore in more mathematical detail at some point.
Andy B





Or on the other hand you can consider looking for a library that lets you do this, I do not know of any but a quick Google search will yield a few results easily.
The sh*t I complain about
It's like there ain't a cloud in the sky and it's raining out  Eminem
~! Firewall !~






Thanks Gerry but in this instance I'll be programming in a nonMicrosoft environment, so making API calls will not be possible, or at least not easily. I have used the Excel solver function in the past for optimization exercises and it is very effective.





Don't get me wrong. I believe Codility proposes interesting problems. This tool might even be a good way of testing candidates' algorithmic skills (not programming skills). My frustration is elsewhere: it's hard, even when it pretends otherwise.
Problems can be one of three categories: "painless", "respectable", and "ambitious".
My experience however is that few of the painless ones actually are painless. Most of them will require a respectable amount of time to solve. A lot of the problems conceal some trick that you need to somehow discover, and you cannot get any hints. Solutions on the internet will instantaneously spoil the whole exercise instead of giving you hints progressively.
Now, even though you got the algorithm right. You are far from being done, as all you have so far isn't worth a penny. The implementation might actually take you more time than finding the algorithm itself. Because, indexes. You misplaced one incrementation, you forgot one, or whatever. The smallest mistake will quickly drop your score down to 0%, you failed, goodbye. You had the right idea though, it's a shame.
And the worst part is: Google won't find anybody that had or is having a similar experience. I'm alone, and it doesn't feel good.





One wrong "increment" can destroy a $$$ industrial process; or kill a patient.
Better on paper, than in the real world.
"(I) am amazed to see myself here rather than there ... now rather than then".
― Blaise Pascal





.. or using the wrong units can prang some very expensive hardware a long long way from home.
Software rusts. Simon Stephenson, ca 1994. So does this signature. me, 2012




